Anglers looking for rainbow trout in the east metro will be dropping their lines in Lake Elmo, at least for the next three years and possibly beyond.

The Minnesota Department of Natural Resources (DNR) last month stocked Lake Elmo with 150 rainbow trout, average 6 to 7 pounds, adding to the thousand one-pounders the DNR put in the lake in October.

The rainbows are going to Lake Elmo because of a newly imposed three-year moratorium on trout stocking in their usual spot in Square Lake, north of Stillwater, said Gerald Johnson, DNR's East Metro Area Fisheries supervisor.

Putting the trout into Lake Elmo will help satisfy the demand for what has become an incredibly popular east-metro trout fishery that had developed at Square Lake, Johnson said. Officials of Washington County, which owns much of Lake Elmo's shoreline and its boat access, agreed to the plan.

"I get more calls about trout fishing than I do for just about any other species," said Johnson, noting that the DNR held public meetings to gauge sentiment on the plan. "Although we were losing the opportunity at Square Lake for a couple of years, we still wanted to provide anglers the opportunity to fish for trout in an area lake. We didn't want to take something away from the angler that is very well received."

The state's inland trout season opens on Jan. 12.

Trout stocking at Lake Elmo may continue even after the three-year period for which it is now planned, Johnson said.

"Lake Elmo is a pretty unique resource here in the Twin Cities -- it has oxygen down deep enough where the water is cold enough to support trout," Johnson said.

The switch to Lake Elmo is part of study to see whether keeping the trout out of Square Lake will improve its clarity, Johnson said. The Carnelian-Marine-St. Croix Watershed District contacted the DNR about the issue 18 months ago, Johnson said, citing study data showing that water clarity in Square Lake had been declining since 1990.

The study found that Square Lake had experienced a decline in large zooplankton, or microscopic crustaceans that are a favorite food of rainbow trout, Johnson said. Those large zooplankton, in turn, feed on smaller phytoplankton, or algae, which can bloom in warm weather and cloud water.

Keeping the trout out of Square Lake may enable the large zooplankton to recover and devour more algae. The less algae, typically the better the water clarity in a lake, Johnson said.

Jim Shaver , watershed district administrator, said he hoped the three-year period would be enough time to prove or disprove a relationship between the rainbow trout, the zooplankton they eat and the water clarity in Square Lake.

In other district lakes, Shaver said, decreasing water clarity has been a result of rising levels of phosphorus, which provides nutrients that drive algae growth. But phosphorous, which can reach lakes from residential or farm runoff, has not been a problem at Square Lake.

The watershed district will begin an intensive monitoring program this winter at Square Lake to try to establish the possible trout-zooplankton-water clarity link, Shaver said. The district will compile annual reports on the data and produce a major final report that will go to a neutral, third-party panel of experts to recommend whether to resume trout stocking in Square Lake.

The district appreciates the opportunity to work with the DNR on the Square Lake issue, Shaver said.

"During this process over the last year it's become clear to me that water quality is becoming paramount at DNR," Shaver said.

The likely options for the DNR, Johnson said, would be to suspend trout stocking in Square Lake indefinitely, offer more of a "put and take" opportunity, stocking fish with the intention that they'll be caught soon, or resume trout stocking at Square Lake as in the past.